TOPIC 1 - EQ1 Flashcards
EQ1: Why are some locations more at risk from tectonic hazards? EQ2: Why do some tectonic hazards develop into disasters? EQ3: How successful is the management of tectonic hazards and disasters?
1.1a What is the global distribution of tectonic hazards?
The pacific ring of fire.
Earthquakes- along plate boundaries (most powerful at destructive and conservative), OFZ and CFZ.
Volcanoes- destructive (composite cone) and constructive (shield) margins and oceanic ridges.
Tsunamis- destructive margins, coastal regions.
1.1a What plate boundary does not lead to volcanic activity and why?
Conservative boundaries due to no subduction or movement apart of the tectonic plates. Subduction zones build pressure which is eventually released as a composite cone volcano and plates diverging from one another at a mid-ocean ridge leaves a gap in the earths crust resulting in shield volcanoes.
1.1b What are the different plate boundaries?
Constructive
Destructive
Conservative
Collision
1.1b Describe a constructive plate margin.
found at mid ocean ridges. shallow hypocentre and low magnitude earthquakes. shield volcanoes. most are submarine. plates are diverging.
1.1b Describe a destructive plate margin.
actively deforming collision locations with plate material melting in the magma (subduction).
deep hypocenter mega thrust earthquakes.
composite cone volcanoes.
1.1b Describe a conservative plate margin.
movement is horizontal (either same direction different speed or different direction).
locked faults.
lithosphere is neither created or subducted.
extensive shallow hypocentre earthquakes.
no volcanic activity.
1.1b Describe a collision plate boundary.
colliding of two continental plates.
no subduction.
fold mountains are formed.
1.1b What are examples of constructive plate margins?
North America and Eurasian Plate.
Mid-Atlantic Ridge Iceland.
1.1b What are examples of destructive plate margins?
Mariana Trench.
Oceanic and continental plate.
The Andes.
1.1b What are examples of collision plate margins?
Eurasian and Indian plate.
The Himalayas.
1.1b What are examples of conservative plate margins?
North American and Pacific Plate.
San Andreas Fault San Francisco.
1.1c What are the causes of intraplate earthquakes.
Earthquakes are caused by stresses within the plate. Since plates move over spherical services, zones of weakness are created.
1.1c What are the causes of intraplate volcanoes?
Earth’s core is hot due to irregular radioactive decay. A mantle plume rising under the surface creates a hotspot on the surface resulting in volcanic activity.
1.2a What are the theories of plate tectonics?
two types of crust: oceanic (underlies ocean basins, thin but dense) and continental (underlies continents, thick but light, floats high on the mantle).
upper mantle: rocks are cool and brittle (can fracture causing earthquakes).
lower mantle: rocks are hot and plastic.
1.2a What are the theories of plate movement?
convection currents and sea floor spreading
Heat which is derived from the earths core (irregular radioactive decay) rises within the mantle to drive convection currents moving tectonic plates.
Sea floor spreading occurs at constructive margins, continuous input of magma forming a mid-ocean ridge, on land a rift valley forms.
1.2a What are the theories of plate movement?
paleomagnetism and slab pull
Paleomagnetism- magnetic strips running parallel to the Mid-Atlantic ridge. iron particles in erupting magma cooled and aligned themselves with the earth’s polarity at the time. used to determine the age of tectonic crust.
Slab pull- gravity causes the denser oceanic crust to be pulled down at the site of subduction.
1.2a Who are the main people involved in the theories of plate movement?
Alfred Wegener: continents were once joined together (Pangea). the plates moved apart due to continental drift.
Harry H Hess: oceanic crust forms along mid-ocean ridges and spread out laterally (sea floor spreading).
Vine and Matthews: paleomagnetism.
The Wilson Cycle: if continents rift apart to form ocean basins then other oceans may close.
1.2b What are the processes operating at constructive margins? What are the hazards and features?
ocean ridge (Mid-Atlantic Ridge). limited seismic activity. shield volcanoes. basic lava (hot and low viscosity). ridge push. sea-floor spreading. convection currents. evidence of paleomagnetism.
1.2b What processes are operating at destructive margins? What are the hazards and features?
deep hypocenter and megathrust earthquakes. tsunamis (due to displacement of water). deep ocean trench. composite cone volcano (acidic viscous lava, violent ash then lava eruptions). fold mountains through orogeny. subduction zone. Benioff zone. Slab Pull. stick and slip. locked faults.
1.2b What processes are operating at collision margins? What are the hazards and features?
fold mountains due to orogeny.
no or very little subduction.
earthquakes.
no volcanic activity.
1.2b What are the processes operating at conservative plate margins? What are the hazards and features?
lots of seismic activity.
locked faults.
stick and slip (build up of tectonic strain, pressure exceeds strength of the fault, rock fractures, elastic energy released, creating seismic waves).
fault line.
1.2c What are the physical processes which impact the magnitude and focal depth of an earthquake?
The Benioff Zone: occurs at destructive margins where subduction occurs. where we find intermediate and deep focused earthquakes. the different speeds and elastic energy stored at this location determine the extent of earthquake magnitude.
1.3a Describe P waves?
primary waves are vibrations caused by compression. they spread quickly from the fault at a rate of 8km/second.
1.3a Describe S waves.
secondary waves move quite slowly at 4km/second. they vibrate at right angles to the direction of travel and cannot travel through liquids.
1.3a Describe love waves.
love waves are surface waves with the vibration occurring in the horizontal plane. they have a high amplitude.
1.3b How does crustal fracturing and ground shaking occur?
how do plate margins produce earthquakes?
the movements are proceeded by a build up of tectonic strain which releases potential elastic energy in rocks.
when the pressure exceeds the strength of the fault, the rock fractures known as stick and slip.
this produces the sudden release of energy, creating seismic waves which move away from the point of fracture (the hypocenter).
the crust rebounds and the ground shakes.
this is known as the elastic rebound theory.
1.3b What is a locked fault?
a fault that is not slipping due to the frictional resistance on the fault being greater than the shear stress across the fault. it is eventually released in a large magnitude earthquake.
1.3b What are the secondary effects of an earthquake?
liquefaction
landslides
1.3b What is liquefaction?
the process by which water saturated material can temporarily lose normal strength and behave like a liquid under the pressure of the strong shaking.
occurs on unconsolidated soil (reclaimed land).
1.3b What are landslides?
slopes weaken and fail due to the strong shaking.
heavy rainfall and therefore saturated land increases this risk.
many destructive earthquakes occur in mountainous areas.
1.3c What are the primary hazards of a volcano?
Lava flows.
Pyroclastic flows.
Tephra and ash falls.
Gas eruptions.
1.3c Describe lava flows.
streams of lava that have erupted from a volcano onto the earth’s surface.
reach up to 1170 degrees and can take years to completely cool.
generally not a threat to human life as move so slowly.
1.3c Describe pyroclastic flows.
a mixture of dense hot rock, lava, ash and gases ejected from a volcano.
move from quickly (100km per hour).
extremely hot (up tp 700 degrees).
1.3c Describe tephra and ash falls.
tephra are pieces of volcanic rock and ash.
large pieces fall near the volcano and cause injury, death and damage to structures.
small pieces (ash) can travel thousands of kilometers.
ash falls cause poor visibility, slippery roads, collapsed roofs, clogged up engines).
1.3c Describe gas eruptions.
The mix normally includes water vapour, sulphur dioxide, hydrogen and carbon monoxide.
Carbon monoxide is associated with most deaths because it is colourless and odourless and can accumulate in valleys undetected by people.
1.3c What are the secondary hazards of a volcano?
lahars and jokulhlaups.
1.3c Describe lahars.
masses of rock, mud and water that travel quickly down the sides of a volcano.
caused when an eruption quickly melts snow and ice or heavy rainfall during or after an eruption erodes loose rock and soil causing it to surge downslope.
1.3c Describe jokulhlaups.
the heat of a volcanic eruption can melt snow and ice in a glacier causing heavy and sudden floods.
can be dangerous as they suddenly release large amounts of water, rock, gravel and ice.
damages land and structures.
1.3d Describe the cause and formation of a tsunami.
Tsunamis are caused by large underwater earthquakes along subduction zones. Energy released during the earthquake causes the sea bed to uplift, displacing the water column above. The displaced water forms tsunami waves.
